The technical scope of the present invention is that of elevation and traverse laying systems for a weapon that ensure its stabilisation.
When a weapon is mounted onto a vehicle, it is well known to provide an elevation and traverse stabilisation system. On a mobile support, that is on a moving vehicle, laying operations become difficult to ensure, since the weapon is subjected to a certain number of disturbances. Firing from such a weapon requires it to be oriented in the direction of the target and this despite any movements, be they linear or angular, of the vehicle. One particularity of a vehicle able to move at high speeds (more than 50 km/h) cross country lies in the stresses it causes to the weapon and to its laying system and which generally correspond to a high level and cover a wide spectrum.
During displacements of the vehicle, these disturbances may notably come from:
the angular velocity of the support of which the weapon is mounted and which reach the weapon via the motorization system,
the linear acceleration applied to the weapon's trunnions and which act upon its orientation by offsetting the centre of gravity,
the angular acceleration applied directly to the weapon by the friction that appears on the trunnions and on the rolling of the turret.
Mounting a weapon onto a vehicle thus requires the installation of an orientation system subjected to a certain number of constraints.
The first is to allow orientation in elevation and in traverse around two axes allowing the required movements. These axes must allow the recoil stresses of the weapon to be transmitted to the support vehicle, in particular by minimising parasite torques in reaction to firing.
Geometric constraints oblige the axis of rotation in elevation to be positioned at the periphery of the turret and towards the rear of the weapon so as to optimise the free space inside the turret. In other words, the axes of rotation in elevation and in traverse are not concurrent.
The geometric organisation of the mounting of the weapon causes two constraints in particular. Firstly, the elevation range joint is generally largely offset to the rear of the weapon, with its effect upon the sensitivity of the weapon's orientation to the vertical accelerations caused when rolling. Secondly, both in elevation and in traverse, the constraints placed upon the motorization systems, but also the necessity of ensuring the sealing of the turret, give rise to frictions whose effects deteriorate the weapon's orientation accuracy.
More particularly, on certain weapon systems, the need to be able to orient the weapon in elevation to several tens of degrees (70° approximately) causes the weapon's orientation to be very sensitive to rolling of the vehicle. In fact, three types of limitations may be found that deteriorate the overall accuracy performances of the weapon. Firstly, the positioning accuracy of the weapon is adversely affected by the influence of friction because of the presence of a large diameter bearing and its associated seals. Thereafter, the offsetting of the weapon's centre of gravity in relation to the position of the joint rapidly deteriorates the quality of stabilisation provided in elevation. Lastly, the motorization torque available on the turret limits the possibility of compensating for the roll effect of the weapon's orientation thereby worsening the level stabilisation error associated with this type of disturbance, in particular if the weapon's angle of elevation increases.
Several methods and devices are known to attenuate the roll effects on the firing performances of a weapon.
A first method consists in measuring the perturbing angular velocity, for example using geometric type means, and using this measurement to control the rotational speed of the motorization system placed between the support and the weapon. It is thus an anticipatory control placed in parallel with a servo control of the weapon's position on an inertial reference whose efficiency is low so as to attenuate the amplitude of the angular disturbances at mean frequencies. Reference may be made, for example, to patent FR-80.21077.
Another method consists in providing motorization means allowing the torque applied to the load to be controlled. This principle is used to improve the efficiency of the reduction of the effects of the angular velocity disturbances. This method is adapted to low offset values. Reference may be made, for example, to patent U.S. Pat. No. 4,387,624.
In these two cases, the weapon's centre of gravity is not far from its trunnion axis.
But when the offset between the axial position of the centre of gravity and the joint axis increases, the performances obtained decrease rapidly through the combination of several mechanisms.
First of all, the offsetting of the centre of gravity increases the effect of vertical acceleration produced (unbalance effect) by rolling on the angular displacement of the weapon.
The increase in motorization torque caused by the needs in dynamic torque (despite the static balancing of the unbalance mass) leads in particular to an increase in the inertia of the motor. The sensitivity of the motorization system to noise at medium frequencies increases as a result, with as a counterpart the necessity to increase the filtering of all the sensors. The stabilisation performances are reduced by the filtering of the sensors.
On certain weapon systems, functional constraints, in particular concerning the weapon replenishment method, add geometric constraints to the offsetting of the centre of gravity, which increase the friction at the trunnions with its effect on the accuracy of the weapon's orientation.
On other systems, to minimise the space required at the rear and under the orientation axis of the weapon, the mounting of the weapon obliges the axis of orientation to be pushed back to the rear of the recoiling mass resulting in further offsetting the centre of gravity with its effect on orientation, in particular when the vehicle is moving.
When the weapon is required to be oriented in elevation away from the horizontal, the drive effect of the weapon caused by the roll of the turret rapidly contributes to the deterioration of the weapon's stabilisation and to the saturation of the turret motorization control in traverse.